Cisco Security Advisory
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CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N/E:X/RL:X/RC:X
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Multiple vulnerabilities in image verification checks of Cisco Network Convergence System (NCS) 540 Series Routers, only when running Cisco IOS XR NCS540L software images, and Cisco IOS XR Software for Cisco 8000 Series Routers could allow an authenticated, local attacker to execute arbitrary code on the underlying operating system.
For more information about these vulnerabilities, see the Details section of this advisory.
Cisco has released software updates that address these vulnerabilities. There are no workarounds that address these vulnerabilities.
This advisory is available at the following link:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-lnt-QN9mCzwnThis advisory is part of the September 2021 release of the Cisco IOS XR Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: September 2021 Cisco IOS XR Software Security Advisory Bundled Publication.
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Vulnerable Products
At the time of publication, these vulnerabilities affected the following Cisco devices if they were running a vulnerable release of Cisco IOS XR Software:
- 8000 Series Routers
- NCS 540 Series Routers that are running the NCS540L images
For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.
Determine the Software Version
To determine whether the device is running a NCS540L software image, use the show version command in the device CLI. If the output indicates LNT, as shown in the following example, then the device is affected by these vulnerabilities:
Router#show version
Cisco IOS XR Software, Version 7.0.1 LNT
Copyright (c) 2013-2019 by Cisco Systems, Inc.Build Information:Products Confirmed Not Vulnerable
Only products listed in the Vulnerable Products section of this advisory are known to be affected by these vulnerabilities.
Cisco has confirmed that these vulnerabilities do not affect the following Cisco products:
- IOS Software
- IOS XE Software
- NX-OS Software
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The vulnerabilities are not dependent on one another. Exploitation of one of the vulnerabilities is not required to exploit the other vulnerability. In addition, a software release that is affected by one of the vulnerabilities may not be affected by the other vulnerability.
Details about the vulnerabilities are as follows:
CVE-2021-34708: Cisco IOS XR Software for Cisco 8000 and Network Convergence System 540 Series Routers Image Verification Vulnerability
A vulnerability in image verification checks of Cisco NCS 540 Series Routers, only when running Cisco IOS XR NCS540L software images, and Cisco IOS XR Software for Cisco 8000 Series Routers could allow an authenticated, local attacker to execute arbitrary code on the underlying operating system.
This vulnerability is due to an unsigned script within the ISO that is not verified when the install request is being processed. An attacker could exploit this vulnerability by modifying an ISO image and then either installing that image as an administrator or placing that image on a file server, which an unsuspecting administrator could then use when upgrading the device. A successful exploit could allow the attacker to execute arbitrary code on the affected device.
Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.
Bug ID(s): CSCvx38902
CVE ID: CVE-2021-34708
Security Impact Rating (SIR): Medium
CVSS Base Score: 6.0
CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:NCVE-2021-34709: Cisco IOS XR Software for Cisco 8000 and Network Convergence System 540 Series Routers Image Verification Vulnerability
A vulnerability in image verification checks of Cisco NCS 540 Series Routers, only when running Cisco IOS XR NCS540L software images, and Cisco IOS XR Software for Cisco 8000 Series Routers could allow an authenticated, local attacker to execute arbitrary code on the underlying operating system.
This vulnerability is due to a race condition that occurs when the install request is being processed, which may allow another authenticated administrator to alter the certificate used to validate whether the installation image has a certificate that is not issued by Cisco. An attacker could exploit this vulnerability by modifying an ISO image and then either installing that image as an administrator or placing that image on a file server, which an unsuspecting administrator could then use when upgrading the device. A successful exploit could allow the attacker to execute arbitrary code on the affected device.
Note: During the installation process, the attacker would need to beat the race condition to change the validated certificate.
Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.
Bug ID(s): CSCvx53064
CVE ID: CVE-2021-34709
Security Impact Rating (SIR): Medium
CVSS Base Score: 6.0
CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N
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There are no workarounds that address these vulnerabilities.
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When considering software upgrades, customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories page, to determine exposure and a complete upgrade solution.
In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.
Fixed Releases
At the time of publication, the release information in the following table(s) was accurate. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information, including SMU availability.
Affected Devices First Fixed Release for These Vulnerabilities Cisco 8000 Series Routers 7.3.15
7.3.2Cisco NCS 540 Series Routers 7.3.2
7.4.1
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The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerabilities that are described in this advisory.
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These vulnerabilities were found during internal security testing.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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Show LessVersion Description Section Status Date 1.0 Initial public release. — Final 2021-SEP-08
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